1. Field of the Invention
The current invention concerns a process for the improvement of the stability properties of solidified radioactive ion exchange resin particles, wherein the resin particles are embedded in a mixture containing an inorganic and/or organic binding agent, which is then left to harden.
2. The Prior Art
In most nuclear power plants organic ion exchange resins in the form of beads or powder are used for the cleaning of the various water circulation systems. In the following, the beads as well as the powder particles of the ion exchange resins are designated as resin particles. The ion exchange resin particles act to retain general impurities in the water circulation systems, and also radionuclides. In this manner, the activity of the circulation systems can be kept within limits. Active ion exchange resins also accumulate in the reprocessing plants. The use of ion exchange resins almost always is carried out in mixed bed processes, i.e., mixed anion and cation exchange resins. Only fresh resins in the OH' or H' form are used in each case, so that no foreign ions are introduced into the circulation systems. The ion exchange resins have to be replaced each time when their capacity has been exhausted by charging with general impurities when they can no longer accept any activity. The replaced ion exchange resins are to be considered mildly to medium active radioactive waste which has to be disposed of.
For a final storage, but even for transport, radioactive waste has to be generally solidified, whereby, for security reasons, varying demands are made with regard to the solidified waste. This includes sufficiently high compressive strength, a good water resistance, sulfate resistance and the lowest possible leach rate. For the solidification of radioactive ion exchange resins, the resin particles are embedded into inorganic and/or organic binding agents, such as cement, bitumen or plastics for the formation of a so-called matrix. It is desired to accommodate the greatest possible amount of waste within a certain matrix volume. The swelling and shrinking behavior of organic ion exchange resins is responsible for the fact that the matrix, after solidification, is possibly not water resistant. For this reason the cement solidification for such resins is often regarded with skepticism. In fact, such a matrix may develop cracks during later storage in water, or even decay, if not special techniques are used during solidification.
With regard to the described facts, the amount of resin for the solidification of resin particles has usually been limited to about 20 kg of dry resin particles per 100 liters of matrix, whereby the resulting compressive strength was a little above 20 N/mm.sup.2. In addition, if the solidification of the cement mixture takes place under water, the matrix also becomes water resistant, unless it is not dried between. With a higher share of ion exchange resins in the matrix, the compressive strength decreases below 10 N/mm.sup.2. But even such a matrix can, under certain circumstances, remain stable at water storage, if there is no drying beforehand. However, if test bodies of such cement solidification procedures are conditioned, e.g., in air with 20% relative humidity, whereby drying causes a weight loss of up to 25%, they are no longer stable for water storage. Their compressive strength decreases already considerably during the drying process, whereby shrinkage tears appear. During subsequent water storage, the test pieces decay in most cases within hours or a few days, or at least large tears appear.